1. Field of the Invention
This invention relates in general to drilling equipment for use in a subsea wellhead, and in particular to a wear bushing which locates on a casing hanger for protecting the casing hanger during drilling operations.
2. Description of the Prior Art
In one type of offshore drilling, the drilling crew will locate a subsea wellhead housing on the sea floor. A riser will extend to a floating drilling vessel at the surface of the water. The drilling crew will lower drill pipe through the riser and wellhead housing to drill the well to a first selected depth.
Then, the drilling crew will lower a string of casing into the well with a casing hanger located at the top of the string. The casing hanger will land in the wellhead housing. The drilling crew pumps cement down the drill pipe, which flows back up the annulus surrounding the casing, cementing the casing string in the well. The drilling crew will than lower the drill pipe with a drill bit on the end for drilling the well to a next selected depth, at a lesser diameter than the upper portion of the well.
Once that depth has been reached, the drilling crew will lower a second and smaller diameter casing string into the first casing string. The drilling crew will land this second casing hanger above the first casing hanger and cement the second casing string in the well.
While the drilling crew drills through casing, there is a possibility that the drill pipe will damage the bore of the casing hanger. It is important to keep the bore of the casing hanger protected for receiving the seals of other equipment, such as a casing hanger or a tubing hanger.
In the prior art, after the casing hanger and casing string are cemented in the well, the drilling crew will lower a wear bushing on drill pipe into the bore of the casing hanger. Once secured in place, the drilling crew retrieves the running tool, then lowers the drill pipe with the drill bit on the lower end for drilling. The wear bushing protects the bore of the casing hanger.
While this is workable, running the wear bushing in a second trip after the casing hanger has been cemented requires additional time. The time could be extensive if the drilling is occurring in deep seas.